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June 18, 2008

Female Chimps Keep Quiet During Mating

by Sam Savage

British researchers said on Wednesday that female chimps keep quiet during sex to keep other females from finding out and punishing them for mating with the best males.

They also discovered that females seem more concerned with having sex with as many mates as possible rather than just finding the strongest male as a way to confuse paternity and secure future protection for offspring.

"They are trying to make the high-ranking males think they are the father," said Simon Townsend, an evolutionary psychologist at the University of St. Andrews in Britain, who led the study. "If you confuse paternity, they are more likely to provide that female with future support."

Townsend said the findings show that chimps can use their calls flexibly in response to social factors while knowing more about the apes could help in conservation efforts.

The mating calls of different animals, especially primates, have interested researchers for some time. A common hypothesis is that females use such calls to advertise to prospective males they are ready to mate, which in turn incites competition that leads to the strongest partner and highest quality offspring.

The findings showed that female chimps are also a touch more savvy about the opposite sex.

"The female chimps we observed in the wild seemed to be much more concerned with having sex with many different males, without other females finding out about it, than causing males to fight over them," Townsend said.

The research team took urine samples from females in a group of about 80 chimps under observation in the Budongo Forest in Uganda able to show when the animals were fertile.

Mating behavior was recorded and the team noted that the female chimps called out for sex partners for as many as 12 days during their reproductive cycle, even though they were only fertile for about 4 days of it.

However, the researchers said they also only called out about a third of the time when mating, much less than other primates. Low-ranking females were also more likely to keep quiet during sex, probably to keep female competitors at bay.

"We think that by being quiet, you are less likely to incite aggression from other females," he said.

The team included researchers from the Max Planck Institute in Lepzig. Their findings were published in the journal PLoS One.